A cathode-ray tube is evacuated to a very low internal pressure and accordingly is subject to the possibility of implosion due to the stresses produced by atmospheric pressure acting on all surfaces of the tube. This problem has been addressed in the art by providing the CRT with an implosion protection band. Such a band is used to apply a compressive force to the sidewall of the CRT to redistribute some of the faceplate forces. The redistribution of the faceplate forces decreases the probability of an implosion of the tube by minimizing tension in the corners of the faceplate. An implosion protection band is also beneficial because it improves the impact resistance of the tube. Glass in compression is stronger than glass which is in tension and the band causes compression in faceplate areas which otherwise would be in tension. Additionally, in the event of an implosion the redistributed stresses cause the imploding glass to be directed toward the back of the cabinet in which the tube is mounted, thereby substantially reducing the probability of someone in the vicinity of the imploding tube being injured.
Mounting lugs, either integral with, attached to, or disposed between the band and the tube faceplate are used to support the tube within the cabinet. Typically, the mounting lugs are positioned at the corners of the tube and aligned along the faceplate diagonals, although other placements of the mounting lugs are known in the art. U.S. Pat. No. 4,295,574, issued to Nakazima et al. on Oct. 20, 1981 discloses a shrinkfit band having integral mounting lugs. A drawback of such a unitized structure is that the lugs must be capable of being bent to properly position them relative to the tube. If the bend radius is too small, the lugs might break. Also if all the lugs are not bent correctly, it might be impossible to accurately mount the tube within the cabinet. Since the lugs must be capable of being bent, the mechanical strength of integral lugs also is suspect.
U.S. Pat. No. 4,222,075, issued to Mitchell et al. on Sept. 9, 1980, discloses a metal implosion protection band which encircles and exerts a compressive force on the sidewall of the faceplate panel. At least one "L"-shaped bracket member, or mounting lug, having a base portion connected to an upstanding attachment portion, with the base portion positioned intermediate the metal band and the corner of the faceplate panel, is used to support the tube within the cabinet. The width of the base portion of the mounting lug is made sufficiently narrow so that the implosion protection band contacts the sidewall of the faceplate panel on the radius of curvature of the corner rather than the flattened portions of the sidewall to enhance the implosion-resistant capabilities of the structures. One shortcoming of such a contact is that the base portion of the mounting lug is merely pinched between the band and the corner of the sidewall and care must be taken to properly locate the center line of the base portion of the lug along the diagonal of the faceplate. If the base portion of the mounting lug is improperly aligned, the attachment portion of the mounting lug will be offset relative to the corresponding attachment point in the cabinet. Additionally, if the base portion of the mounting lug is improperly positioned relative to the faceplate diagonal, the compressive forces on that corner of the faceplate will be unequal.
U.S. Pat. No. 4,210,935 issued to Mitchell et al. on July 1, 1980, discloses an "L"-shaped bracket, or mounting lug, used in conjunction with a rimband-type implosion resistant cathode-ray tube. In the patented structure, an adhesive is applied to the sidewall of the tube adjacent to the faceplate. A pair of metal rimbands overlie the adhesive and encircle the sidewall. The "L"-shaped mounting lugs each have a rounded base portion which is affixed to the rimband by a tension band which encircles and compresses the base portion of the mounting lug and contacts the rimband on the radius of curvature of the corner prior to the flattened portion of the sidewall. The latter-described structure has the same shortcomings described with respect to U.S. Pat. No. 4,222,075.
U.S. Pat. No. 4,360,837, issued to Kreidler et al. on Nov. 23, 1982, discloses a rimband implosion protection structure in which discretely formed slots in the rimband components engage compatibly with base portions of the mounting lugs to laterally position the mounting lugs prior to tightening the overlying tension band. One drawback of the disclosed structure is that the lug-affixing operation is labor intensive since the contoured base portions of the mounting lugs must be forced through the rimband slots and properly seated before the bands are attached to the tube. Forcing the base portions of the lugs through the slots in the rimbands also present the opportunity to damage or distort the corners of the rimband, thus, adversely affecting the compressive effect of the rimband on the underlying sidewall.
U.S. Pat. No. 3,317,172, issued to Balint on May 2, 1967, shows, in one embodiment, the base of a mount lug riveted or spot welded to an overlying tension band. The patent also shows the mounting lugs positioned adjacent to the flattened portion of the faceplate sidewall adjacent to the corner of the faceplate. A drawback of this structure is that the inward force on the portion of the tension band overlying the flat sidewall is proportional to the sine of the angle and that for small angles the inward force is very small. For example, if the angle of the sidewall is the degree (sine 0.017) and the force on the band is 3000 lb., the inward force is only 51 lb. Since a tension band is relatively thin and flexible, the weight of a large tube may be sufficient to offset the force of the band and cause the band to lose contact with the sidewall thereby jeopardizing the integrity of the implosion band.